1. Technical Field
The present invention relates to a control valve, which is arranged in a hydraulic system to be arranged in a construction machine or the like and is operable responsive to a pilot pressure to control a flow of pressure fluid to be supplied to an actuator.
2. Background Art
Hydraulic apparatuses, for example, construction machines and the like often make use of a system that a flow rate of working fluid is controlled by a control valve operable responsive to a pilot pressure and the pilot pressure is outputted, as is, as a control pressure to control a pressure and flow rate of pressure fluid to be delivered from a hydraulic pump. In this instance, it is a common practice to control plural spools, which are arranged in association with a single hydraulic pump and are housed within the control valve, to effect distribution of a flow rate. Adopted here is a system that the highest one of pilot pressures for actuating the plural spools, respectively, is transmitted to a delivery control device for the hydraulic pump by way of a shuttle valve or the like. It is generally a hydraulic remote control valve that controls the plural pilot pressures, and as is shown in JP 3-59502, the shuttle valve which selects the highest one of the pilot pressures is generally arranged as an integral element inside the hydraulic remote control valve.
FIG. 3 is a circuit diagram of a conventional technique of this sort, namely, of a hydraulic system including a conventional control valve.
The conventional technique shown in FIG. 3 is provided with a variable displacement hydraulic pump 61, a control valve 62 having spools 57,59 for controlling flows of hydraulic fluid delivered from the hydraulic pump 61 and supplied to unillustrated actuators such as hydraulic cylinders, and a hydraulic remote control valve 70 for producing pilot pressures for actuating the spools 57,59 in the control valve 62.
The hydraulic remote control valve 70 includes a control lever 50 for controlling the spool 57, a control lever 51 for controlling the spool 59, hydraulic pilot valves 50a,50b operable in association with pivotal control of the above-mentioned control lever 50, and hydraulic pilot valves 51a,51b operable in association with pivotal control of the above-mentioned control lever 51.
The pilot valve 50a and a pressure fluid port, which is in communication with one 57a of pressure fluid control compartments in the spool 57, are connected to each other through a pilot line 56a, while the pilot valve 50b and a pressure fluid port, which is in communication with the other pressure fluid control compartment 57b in the spool 57, are connected to each other through a pilot line 56b. Similarly, the pilot valve 51a and a pressure fluid port, which is in communication with one 59a of pressure fluid control compartments in the spool 59, are connected to each other through a pilot line 58a, while the pilot valve 51a and a pressure fluid port, which is in communication with the other pressure control compartment 59b in the spool 59, are connected to each other through a pilot line 58b. Of the above-mentioned pilot lines 56a,56b,58a,58b, portions exposed to the outside of the hydraulic remote control valve 70 make up external lines and are formed, for example, of pressure fluid hoses having flexibility.
Further, the above-mentioned hydraulic remote control valve 70 is of a construction that includes, as integral elements, a first shuttle valve 52 for selecting fluid on a side of higher pressure one of the pilot lines 56a,56b, a second shuttle valve 53 for selecting fluid on a side of higher pressure one of the pilot lines 58a,58b, and a third shuttle valve 54 for further outputting higher one of the pilot pressures outputted from the first and second shuttle valves 52,53, respectively.
In addition, the conventional hydraulic system is also provided with a line 60 for transmitting the pilot pressure, which has been outputted through the third shuttle valve 54, as a control pressure for the hydraulic pump 61. This line 60 is also in the form of an external line, and comprises a pressure fluid hose having flexibility.
The hydraulic remote control valve 70 is generally arranged on a left-hand or right-hand side of the driver""s seat. According to the conventional art, there is a tendency that, as shown in FIG. 3, more pressure fluid hoses tend to be connected to the hydraulic remote control valve 70, so that a limitation tends to be imposed on a space for its arrangement. In other words, the arrangement and design tolerance of the hydraulic remote control valve 70 tends to become smaller. Incidentally, five external lines extend out as pressure fluid hoses in total in the embodiment illustrated in FIG. 3, including the four pilot lines from the hydraulic remote control valve 70 and the single line from the third shuttle valve 54.
As apparatuses making use of the hydraulic remote control valve 70 of this type, on the other hand, there are, for example, mini power shovels such as that disclosed in JP 8-137567. In mini power shovels of this type, control levers for operating a remote control valve are arranged movably in many instances in view of operator""s convenience upon ingress to and egress from the operator""s seat. An example of these mini power shovels is illustrated in FIG. 4.
As is shown in FIG. 4, the mini power shovel is provided with a travel base 101, which includes a pair of crawler treads, and a swivel superstructure 102 arranged on the travel base 101. On the swivel superstructure 102, an operator""s seat 103 is disposed, and a canopy 104 is arranged above the operator""s seat 103 such that a roof 104a covers the operator""s seat 103. A swing post 105 is arranged on a front part of the swivel superstructure 102. A boom 106 is connected to the swing post 105. The boom 106 is turnable in a vertical direction, and is also turnable in a horizontal plane by way of the swing post 105.
Arranged in front of the operator""s seat 103 are a left drive lever 107a and a right drive lever. The left drive lever 107a is used to operate an unillustrated left drive motor which serves to drive the left-hand crawler tread of the travel base 101, while the right drive lever is employed to operate an unillustrated right drive motor which serves to drive the right-hand crawler tread of the travel base 101. Arranged on a forward left-hand side of the driver""s seat 103 is a left control device for operating, for example, unillustrated boom and bucket cylinders adapted to drive the boom 106 and an unillustrated bucket, respectively; namely, a left console 108 having a left control lever 108a. Arranged on a froward right-hand side of the operator""s seat 103 is a right control device for operating, for example, unillustrated arm cylinder and swivel motor adapted to drive an unillustrated arm and the swivel superstructure 102, respectively; namely, a right console having a right control lever. In addition, a left gate lock lever 110a which makes up a jump lifter is arranged on the side of the left console 108, and a right gate lock lever which makes up another jump lifter is disposed on the side of the right console.
In the mini power shovel constructed as described above, an operator who has operated it in the operator""s seat 103 turns the left gate lock lever 110a in a clockwise direction as viewed in FIG. 4 (to a position indicated by alternate long and short dash lines in the figure) when the operator wants to egress, for example, from the left side where the left console 108 is located. When the left gate lock lever 110a is caused to turn as mentioned above, the control lever 108a is also caused to jump up rearward so that a foot area, specifically the space on a forward left-hand area of the operator""s seat 103 becomes wider, thereby facilitating an egress of the operator who has sat in the operator""s seat 3.
Due to the above-mentioned tendency of arrangement of more pressure fluid hoses, however, such pressure fluid hoses still interfere with operator""s stepping up or down even when the foot area has become wider. Further, due to an additional weight of such pressure fluid hoses, large operating force is indispensable upon operating the gate lock lever 110a. An improvement has hence been desired in operability. It has also been pointed out that due to heat from these pressure fluid hoses, the operator""s seat tends to become hot, leading to a deterioration in the working environment of the operator.
These days, there is also a tendency that the dimensions of the hydraulic remote control valve 70 are limited small to assure a sufficient space around the operator""s seat. Because more pressure fluid hoses are arranged as mentioned above, work which is required to connect these pressure fluid hoses to the hydraulic remote control valve 70 tends to become more irksome, resulting in a problem of an increased assembly manpower.
The present invention has been completed in view of the above-described problems of the prior art, and as an object thereof, has the provision of a control valve which can be constructed with external lines as few as needed essentially.
To achieve the above-described object, the present invention furnishes a control valve provided with a plurality of spools movably arranged within a valve body, movements of the spools being effected by pilot pressures, respectively, characterized in that a shuttle valve for selecting higher one of the pilot pressures, which cause the spools to move, respectively, is arranged within a main body of the control valve.
The main body of the control valve may comprise the valve body and spool covers, the value body of the control valve may be provided with a pump port which is connected to a variable displacement hydraulic pump, and an actuator port connected to an actuator. The spool covers may be arranged on an longitudinal extension of the spools and on opposite sides of the valve body, respectively, and the shuttle valve may be arranged on at least one of the spool covers.
One of the spool cover of the main body of the control valve may be provided with a line which is a first pressure fluid port connected to a delivery control device for the variable displacement hydraulic pump. Further, the spool covers may each be provided with two pressure fluid ports connected as second and third pressure fluid ports to a hydraulic remote control valve, and the shuttle valve may be arranged between the second and third pressure fluid ports. Here, the second and third pressure fluid ports may be arranged adjacent to each other.
In addition, a shuttle valve for transmitting a control pressure to the variable displacement hydraulic pump may be arranged within the main body of the control valve.
When constructed as described above, the spools are actuated by pilot pressures transmitted as a result of control of the hydraulic remote control valve, whereby drive of the actuator, said drive being governed by the actuation of the spools, is controlled. Further, higher one of the pilot pressures applied to the spools is outputted from the shuttle valve arranged within the control valve, and is transmitted as a control pressure for the delivery control device. Accordingly, lines directly associated with the actuation of the spools are only required as external lines connected to the hydraulic remote control valve, and as a line for transmitting the pilot pressure as a desired control pressure, one connecting the control valve with an equipment desired to be controlled is only required. This makes it possible to reduce to a minimum the number of external lines connected to the hydraulic remote control valve.